I buy 7.62 x 39 and 5.56 in bulk. I've used the Russian "Bear" versions in both calibers with no problems except if I get too carried away, a lacquered case will stick in an overheated chamber on the AK, occasionally. Haven't had the problem in the mini-14, not sure why.
Ammoman.com is good, Cheaper Than Dirt is good but more expensive. I ran across some Federal American Eagle in the white 100-round boxes at an Academy store for $30.00. They sold out pretty quickly; may have been an error in pricing?
I get mine mostly from local gunshows, if I know the dealer. On the last day of the local show in August, I found some nice bargains in Silver Bear 7.62 x 39 hollowpoints.
As has been said, "It all goes bang and flies reasonably straight".